1. Field of the Invention
The present invention relates to an apparatus capable of transmitting a rotary power between an input rotary member and an output rotary member eccentric from each other and changing the eccentricity inbetween.
2. Related Art
In a rotary machining by a milling machine or the like, a plurality of diameters may be machined by a tool of one kind by changing the turning radius of the edge of the tool. In this case, not only the machining radius can be easily changed but also a complicated machining such as the cutting of a tapered face can be performed, if the structure, in which the edge is changed in position by attaching and detaching it to and from the tool body, is replaced by a mechanism for moving the edge radially of the tool body.
The mechanism capable of changing the turning radius of the tool edge continuously is disclosed in Japanese Patent Laid-Open No. 51211/1989. In the apparatus disclosed, a cylindrical holder body, as mounted on the rotary spindle of a machine tool, is provided at its leading end portion with a radially directed slide guide, with which the tool is movably engaged. Moreover, the holder body is equipped therein with a motor and a feed screw mechanism to be actuated by the motor, so that the tool may be moved along the slide guide by the feed screw mechanism. In the disclosed apparatus, therefore, the tool is moved along the slide guide by energizing the motor so that the edge position in the radial direction of the rotary spindle can be continuously changed even while the rotary spindle is rotating.
However, the aforementioned construction of the prior art is disadvantageously complicated because the motor and the feed screw mechanism have to be disposed in the rotary spindle. Since the center of rotation of the rotary spindle fails to be aligned with the center of gravity, moreover, the eccentric force for the eccentric load grows higher according to the increase in the number of rotation so that the number of rotation of the rotary spindle is disadvantageously restricted so as to prevent the vibration and to keep the rotating accuracy. In order to change the edge position or the cutting radius during the cutting operation, the motor in the rotating rotary spindle has to be energized. For this energization, contacts such as slip rings or brushes are mounted on the outer circumference of the rotary spindle. When this rotary spindle is turned at a high speed, however, insufficient contact or contact wear may probably occur to raise problems in the reliability and the durability.
Here, the Oldham's coupling, a universal joint or a flexible cylinder is known as the mechanism for transmitting a torque between the input and output sides which are eccentric from each other. However, these mechanisms of the prior art may be restricted in the transmittable torque and the number of rotation and may have to change the spacing between the input side member and the output side member so as to change the eccentricity. If this eccentricity is to be changed during the rotation, moreover, the necessary mechanism is disadvantageously complicated.